With the MTurk API it is possible to create notifications that use the Amazon SNS or SQS services, but "Notifications are associated with a HIT type." The HIT type is a non-optional parameter in the creation of a notification using the UpdateNotificationSettings operation. This apparently means that there's no way to set a notification for creation of new HITs unless the HITTypeID is already created and manually entered into the UpdateNotificationSettings operation. In practice, this appears to mean that it is not possible to set up a notification that is generally associated with the creation of new HITs, and in fact it seems like the cases where it is possible to use notifications are actually, arguably, a minority, because when new HITs are created with the CreateHIT operation, which is a normal thing to do, the HITTypeID is created automatically.
I am not that much of an expert on AWS in general so I am wondering if there is some method for setting up event triggers other than the notification system documented at the first link above. It seems like it would be a widely useful and in-demand feature to be able to have notifications or event triggers associated with the general case of HIT creation, rather than (apparently) having it restricted to only the cases where the HITTypeID is known in advance and manually entered, so I am wondering if I am simply missing something because of my limited knowledge of how AWS works?
Thanks very much for any advice, and apologies if my limited knowledge of AWS means that this question is missing something obvious...
Well, I didn't get any replies here in almost two weeks, but I had a chance to talk directly to an engineer at Amazon MTurk and so I can answer it myself: Indeed, there is no way to set up notifications without already knowing the HIT Type ID. So there's no event-driven way to make a web app that "knows" whenever a new HIT is launched. However, I am assured that it is fine to poll the ListHITs API operation and look for new HITs this way. Although ListHITs can take a while to run (for me, it's about 40 seconds to retrieve a total of about 2000 HITs) the engineer suggests that it's unlikely to run into API rate limits for plausible polling intervals.
It also appears (although undocumented) that ListHITs returns HITs in reverse chronological order. So one can request pages until one sees an already-known HIT and then stop requesting pages of results.
In conclusion, although it is not possible to use the notifications system the way I want, I can solve my problem by polling every (x) minutes and using the aforementioned approach to find the new HITs each time.